Drafting machine

ABSTRACT

The disclosed drafting machine comprises a drafting head coupled to a main carriage supported on a main rail for movement parallel to a transverse axis. Parallel top and bottom rails support main rail carriages for movement parallel to a longitudinal axis of the main rail pursuant to positioning the drafting head to any point on the drafting surface. A drive train is incorporated for precise point to point positioning of the drafting head either under manual positioning control or automatic positioning control on the basis of numerical positioning data inputs.

United States Patent 1 [111 3,714,714 Bullard, III 51 Feb. 6, 1973 1 DRAFTING MACHINE 3,032,881 5/l962 Fengler ..33/23c [76] Inventor: Edward P. Bullard, III, MTD Bldg, 171 Spring Hill Rd, Trumbull, Conn.

[22] Filed: Feb. 12, 1971 [21] App1.No.: 114,832

[52] US. Cl [51] Int. Cl. ..B43I 13/02 [58] Field of Search ..33/76, 79, 80, 23 C, 18 R, 33/1 M, 189

[56] References Cited UNITED STATES PATENTS I 1,180,083 4/1916 Shiley ..33/79 R 1,006,704 10/1911 Villeneuve ....33/79 R 3,398,452 8/1968 Little et al. ....33/18 R 2,922,333 1/1960 Suback et al.... .....33/1M 3,153,284 10/1964 Harris ....33/79 R FOREIGN PATENTS OR APPLICATIONS 754,445 8/1956 Great Britain ..33/79 R Primary Exa'miner-I-Iarry N. Haroian Attorney-St. Onge Mayers & Reens [57] ABSTRACT The disclosed drafting machine comprises a drafting head coupled to a main carriage supported on a main rail for movement parallel to a transverse axis. Parallel top and bottom rails support main rail carriages for movement parallel to a longitudinal axis of the main rail pursuant to positioning the drafting head to any point on the drafting surface. A drive train is incorporated for precise point to point positioning of the drafting head either under manual positioning control or automatic positioning control on the basis of numerical positioning data inputs.

12 Claims, 14 Drawing Figures PATENTEB FEB I 6 I975 SHEET 10F 8 mm 0E wmw INVENTOR.

Edward BBuZZard, H

RNIEYS PATENTEU FEB 6 I973 SHEET 70F 8 www Q o 0 1 4 4 4 4 v :iiisi...

2 ILF PATENTED FEB 6 I973 SHEET 8 BF 8 DRAFTING MACHINE BACKGROUND OF THE INVENTION Drafting machines have been used for many years by draftsmen to assist them in making technical drawings more rapidly. The typical drafting machine comprises a drafting head having orthogonal straightedges. In one type of drafting machine the drafting head is connected to an articulated, pivotal arm consisting of a series of parallel links, which attempt to maintain the spatial orientation of the straightedges reasonably constant regardless of the position of the drafting head on the drawing surface. Unfortunately, the articulated and elongated nature of the pivotal arm readily accommodates a certain degree of flexure, and thus skewing of the spatial orientation of the straightedges is common as the drafting head is moved about. Even if parallelism of the drafting head is relatively precise, it can readily be distorted by inadvertent pressures exerted by the draftsman. Thus intended parallel lines may not be precisely so. In many situations such deviations may be intolerable.

In another common type of drafting machine, a longitudinal top rail supports and guides a transverse main rail for longitudinal movement. The main rail, in turn, supports and guides the drafting head for transverse movement. Since the bottom end of the main rail is supported on a flat track, the perperidicularity of the main rail to the top rail is dependent solely on the mounting of the top end of the main rail to the top rail. The requisite elongation of the main rail renders precise perpendicularity virtually impossible to maintain.

Moreover, when using drafting machines of this type, all dimensions must be scaled off by the draftsman. Consequently, there are always the problems of inconsistency in scaling, difficulty in reading the scale, and outright erroneous scaling. Thus, drafting machines currently available to draftsmen relieve little of the tedium involved in making technical drawings and do not prevent or even materially reduce the possibility of error.

It is accordingly a general object of the present invention to provide a drafting machine which, in the hands of a draftsman, provides for the production of more accurate drawings and in considerably less time than has been possible with currently available drafting machines. The drafting machine of the present invention greatly minimizes the major areas of human error, eliminates many sources of fatigue, and permits the draftsman to concentrate on the important aspects of drafting by relieving him of many of the routine functions normally associated with the drafting art.

Other more specific objects of the invention will in part be obvious and will in part appear hereinafter.

SUMMARY OF THE INVENTION drafting machine includes a drafting head which is coupled to a main carriage mounted on a main rail for movement in a transverse direction over a drafting surface. The main rail is adapted with a carriage at each end which are in turn mounted on top and bottom rails to accommodate longitudinal movement of the main carriage.

Precision circular pitch rack gears are mounted by the top and bottom rails, and each is engaged by an identical pinion gear carried by the main rail carriages. The pinion gears are maintained in a constant angular relation by identical gearing and a cross shaft journalled by the main rail carriages. The ends of the main rail must therefore move in concert and all bending moments and stresses on the main rail are canceled with the result that perpendicularity of the main rail to the top and bottom rails is always assured.

A precision circular pitch rack gear also mounted by the main rail is meshingly engaged by a pinion carried by the main carriage. A pair of handwheels are mounted by the main carriage. One handwheel is coupled by the cross shaft to the pinions of the main rail carriages meshing with the top and bottom rail racks, such that rotation thereof moves the main rail and drafting head longitudinally. A graduated dial carried on' the longitudinal handwheel shaft provides a readout of the increment of longitudinal movement of the drafting head induced by rotation of the longitudinal handwheel.

Similarly, the other handwheel is coupled to the mainv ty of scaling off dimensions. Instead the desired dimensions are read off the dials as the handwheels are rotated pursuant to positioning the drafting head accordingly. Drafting head positioning to within five thousandths of an inch is readily achieved.

The present invention also contemplates automatic positioning of the drafting head on the basis of numerical control positioning data inputs. Instead of positioning the drafting head by rotation of the handwheels, the desired increments of drafting head movement in the longitudinal and transverse directions are entered through digital switches. The digital inputs are supplied to a control network for a stepping motor. The motor is drivingly coupled through a first clutch, brake and cross shaft to the pair of main rail carriage pinions meshing with the top and bottom rail racks. The motor is also drivingly coupled through a second clutch, brake and cross shaft to the main carriage pinion meshing with the main rail rack. The clutches are engaged, the brakes released, and the motor is energized to successively step off the increments in the longitudinal and transverse directions entered by the digital switches. Upon ultimate positioning of the drafting head in each direction, the brakes are engaged prior to releasing the clutches to prevent inadvertent movement of the drafting head. Different drawing scales are achieved by changing the motor drive ratio. Depending on the scale being used, discreet resolution under automatic control varies from 0.003 inch to 0.00025 inch.

Ineither the manual or automatic drafting machine embodiments of the invention, the longitudinal and transverse brakes may be released, and the drafting head directly manipulated with minimum effort to various positions. Movement of the drafting head is with such mechanical ease that it is preferred to include a counterweight system for counterbalancing the weight of the main carriage and drafting head when the drafting surface is inclined.

The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description'taken in connection with the accompanying drawings, in which: 6

FIG. 1 is a perspective view of an automatic drafting machine constructed according to one embodiment of the invention;

FIG. 2 is .a sectional view consisting ofFIGS. 2A and 2B in juxtaposition, as taken along line 2-2 of FIG. 1;

FIG. 3'is a sectional view taken along line 3-3 of FIG. 2A;

FIG. 4 is a sectional view taken along line 4--4-of FIG. 2B;

. FIG. 5 is a sectional view, partially broken away, taken along line 5-5 of FIGS. 2A and 2B;

bly and filed concurrently herewith, generally in cludes a pair of straightedges 26a and 26b secured to support member 26c in orthogonal relationship to each other. The support member is formed having an annular protractor rail 26d which is accommodated in an annular track 26 included in a frame 26]. Frame 26f, in turn, is pivotally connected to spaced brackets 27 extending laterally from main carriage 28 through the provision of a frame mounted pin'26g received in a notch formed in each main carriage bracket. Thus the drafting head may pivot upwardly away from the drafting surface or disconnected altogether from the main carriage 28, but is otherwise rigidly connected thereto.

The centers of curvature of protractor rail 26d and track 26 coincide and are precisely located at the intersection or vertex of straightedges 26a and 26b. The straightedges terminate short of their vertex leaving a gap which is occupied by a transition rule 26h pivotally connected to support member 260. Transition rule 26h has two positions; one position with one of its straight I side edges aligned with the ruling edge of straightedge 26a and another position with the other of its straight side edges aligned with the ruling edge of straightedge 26b. Thus transition rule 26h serves to effectively extend the ruling edges of straightedges 26a and 26b FIG. 6 is a sectional view taken along line 6.6 of 1 FIG. 2A;-

FIG. 7 is a sectional view taken'along line 7--7 of FIG. 5;

FIG. 8 is a sectional view taken along line 88 of FIG. 5;

' FIG. 9 is a wiring and schematic block diagram of the, electrical controls for the automatic drafting machine of FIG. 1; I j

FIG. 10 is a sectional view comparable to FIG. 5 illustrating a strictly manual drafting machine constructed according to an alternative embodiment of the invention; I

FIG. llis a sectional view taken along line -11 of FIG. 10; and

FIG. 12 is a side elevational view of the drafting machine illustrating the essential features of a counterweight system usable with both the automatic and.

manual embodiments of the invention.

Similar reference characters refer to similar parts throughout the several views of the drawings.

DETAILED DESCRIPTION face 24. A drafting head, generally indicated'at' 26,

. rests on the drafting surface and is pivotally connected to a main carriage, generally indicated at 28, which, in

turn, is supported on a main rail 30 for transverse movement over the drafting board 20. Drafting head 26, fully disclosed and claimed in m copending application entitled Drafting Head Assemthrough the gap area therebetween', thereby facilitating the drawing of lines up to and through their vertex.

Moreover, the protractor rail 26d carried by support member 26c is movable in track 26e in frame 26f to revolve the support member and thus straightedges 26a and 26b about their vertex to accommodate the drawing of radial lines therethrough.

The foregoing brief description of drafting head 26 is believed adequate for a complete understanding of the construction and operation of the drafting machine to be considered. Further details of the drafting head may be obtained by reference to the above-noted-copending application, whose disclosure is specifically incorporated herein by reference. However, it will be appreciatedthat the drafting machine of the present invention may incorporate a variety of drafting heads to advantage.

Still referring to FIG. 1, the upper end of main rail 30 is mounted by an upper carriage 32 in turn supported by a top rail 34 attached to the drafting board along its upper side. A bottom rail 36 attached to drafting board 20 along its lower side supports a lower carriage 38 mounting the lower end of main rail 30. Main rail carriagcs32 and '38 are movable along'top rail 34 and bottom rail 36, respectively, in order to position the draft ing head 26 and main carriage 28 longitudinally over the drafting surface 24. s

It is thus seen that main rail 30 moves longitudinally on the top and bottom rails, and the main carriage 28 moves'transversely on the-main rail to position the switches for initiating and controlling positioning movements of the drafting head 26 inthe longitudinal and transverse directions. The numerical, control unit input 40 is electrically linked over a cable 42 to a motor control network housed in base 22. The motor control network controls a stepping motor mounted by upper main rail carriage 32; the motor being hidden in FIG. I by a protective housing 44. As will be seen in the description to follow, the stepping motor is drivingly connected to main rail carriages 32 and 38 and main carriage 28 so as to translate drafting head 26 in the longitudinal and transverse directions; the magnitudes of these movements being determined by the settings of the digital switches of the numerical control input unit 40.

A suitable stepping motor for use in the present in vention is a model HS2S SLO-SYN Precision Stepping Motor manufactured by the Superior Electric Company of Bristol, Connecticut. This company also makes suitable stepping motor control networks for use in the automated drafting machine embodiment of the present invention. It will be appreciated that there are numerous makes and types of stepping motors and stepping motor control networks applicable to the present invention. Also, the automatic drafting machine of the invention may be adapted with analog positioning techniques using a servo motor network.

Referring now to FIGS. 2A and 2B, which are juxtaposed in the manner shown in FIG. 2, the stepping motor, indicated at 50 in FIG. 2B, is mounted by an upright plate 52 supported by the main rail adjacent its upper end. The output shaft 50a of the stepping motor carries a gear 54 which engages a gear 56 secured on the left end of a shaft 58 journalled by plate 52 and a mounting plate 60 of upper main rail carriage 32, also attached to the upper end of main rail 30. The right end of shaft 58 extending through and beyond mounting plate 60 carries a gear 62 adapted for meshing engagement with gear 64 (also FIG. 4) secured on the right end of a shaft 66 also journalled by mounting plates 52 and 60. It is contemplated that gears 54 and 56, as well as gears 62 and 64, may be replaced with gear sets of various drive ratios to thus establish different drawing scales automatically without having to scale the numerical inputs entered at numerical control input unit 40 up or down.

As best seen in FIG. 4, shaft 66 mounts a second gear 68 adapted for meshing engagement with a pair of ring gears 70 and 72, which are in turn mounted by the input drive members of a pair of electromechanical clutches 74 and 76, respectively. Returning to FIG. 2B, the-output shaft 78 for clutch 74 extends coaxially through the clutch bodyand ring gear 70 carried on its input drive member. The left end of clutch output shaft 78' is connected by a coupling 79 to the brake shaft 80 of an electromechanical brake '82 supported by mounting plate 52. In identical fashion, the output shaft 84 of clutch 76 extends coaxially through the clutch body and ring gear 72 on its input drive member as seen in FIG. 4. The other end of clutch output shaft 84 from that shown in FIG. 4 is coupled to the brake shaft of an electromechanical brake which occupies the same position relative'to clutch 76 as does brake 82 relative to clutch 74. This brake is indicated schematically at 88 in FIG. 9, together with the schematic representations of clutches 74, 76 and brake 82.

As best seen in FIG. 4, output shaft 78 of clutch 74 carries a pinion gear 90 on its right end, as seen in FIG. 2B, which is adapted for meshing engagement with an idler gear 92. In FIG. 28 it is seen that the idler gear 92 is mounted on a stub shaft 93 journalled at its ends in mounting plate and a secondary mounting plate 94. Idler gear 92, in turn, meshes with a pinion gear 96 mounted on an elongated cross shaft 98 which extends the length of main rail 30, as seen in FIGS. 2A and 2B. The right end of cross shaft 98 is journalled in a bearing 99 fitted in a through bore 100 formed in mounting plate 60. The left end of cross shaft 98 is journalled in a bearing 102 mounted by a plate 103 (FIG 5), included as part of the lower carriage 38 for main rail 30. As will be seen, cross shaft 98 is the transverse cross shaft which, upon rotation by motor 50, produces transverse movement of the main carriage 28 on main rail 30.

Returning to FIG. 4, output shaft 84 of clutch 76 also carries a pinion gear 106 which engages an idler gear 108 journalled between mounting plates 60 and 94 (FIG. 2B). Idler gear 108 engages a pinion gear 110 mounted on a second cross shaft 112, also extending through main rail 30 in side by side relation with cross shaft 98, as best seen in FIG. 5.

Referring to FIGS. 28 and 4, pinion gear 110 on cross shaft 112 engages an idler gear 114 journalled between mounting plates 60 and 94. Idler gear 114 engages a gear 116 mounted on a shaft 117 journalled by bearings fitted in through bores formed in mounting plates 60 and'94. The left end of shaft 117 beyond mounting plate 60 carries a pinion gear 120 adapted for meshing engagement with an elongated, circular pitch rack gear 122 secured to the undersideof the upper laterally extending portion 34a of the channel-shaped top rail 34. As seen in FIG. 4, rack gear 122 is substantially coextensive with the length of top rail 34.

The upper main rail carriage 32, seen in FIG. 2B, includes a laterally extending bracket 124 secured to mounting plate 60 for the purpose of mounting a pair of longitudinally spaced rollers 126 (one seen in FIG. 2B) which roll along the upper front surface of top rail 34. In addition, mounting plate 60 carries a pair of longitudinally spaced rollers 128 which ride on the upper surface ofthe laterally extending top rail portion 34a (see also FIG. 4). Mounting plate 60 is further notched, as indicated at 130 in FIG. 4, to facilitate mounting a pair of rollers 132 adapted to roll along the edge of laterally extending top rail portion 34a.

It is thus seen that upper carriage 32 for main rail 30 is supported by the top rail 34 for longitudinal movement therealong. The various carriage rollers 126, 128 and 132 insure that the carriage movement is smooth and substantially effortless, and is accurately guided by top rail 34 without any possibility of binding or skewing. Longitudinal movement of upper carriage 32 is induced by rotation of pinion 120 in meshing engagement with the elongated rack gear 122; pinion rotation being motivated either from motor 50 during automatic operation of the drafting machine, by rotation of a longitudinal handwheel at the main carriage 28, or. by longitudinal positioning forces exerted on the main rail, main carriage and drafting head.

As seen in FIGS. 2A and 3, the left hand end of cross shaft 112, seen also in FIG. 5, is journalled at its left end in a bearing fitted in mounting plate 103 of lower carriage 38. Just inwardly from its left end, cross shaft 112 carries a pinion gear 142 which engages an idler gear 144 journalled between mounting plate 103 and a secondary mounting plate 146, also attached to the lower end of main rail 30. Idler gear 144, in turn, engages a gear 148 mounted on a shaft 150 also journalled by mounting plates 103 and 146. Shaft 150 carries a pinion gear 152 which engages an elongated, circular pitch rack gear 154 mounted by and coextensive with elongated bottom rail 36.

Bottom rail 36 is formed having a longitudinally extending recess 156 in which are fitted coextensive upper and lower inserts 156a and 156b to provide a precise longitudinal guideway for a roller 158 carried on pinion gear shaft 150. It is thus seen that upon rotation of cross shaft 112, either by motor 50 or the main carriage handwheel, pinion gear 152 of the lower carriage 38 is rotated, and its meshing engagement with rack gear 154 induces longitudinal movement of the lower carriage 38; this longitudinal movement being supported by roller 158' operating in notch 156 of bottom rail 36. Since the gearing in the upper and lower main rail carriages from cross shaft pinions 110 and 142 on down to rack gears 122 and 154 is identical in each case, the ends of the main rail are constrained to always move equal amounts and therefore, the transverse relationship of the main rail 30 relative to the drafting board 20 is precisely maintained throughout the entire range of its longitudinal movement.

Main carriage 28, as seen in FIGS. 2A, and 6, comprises an open rectangular frame, generally indicated at 166, having a pair of sidewalls 168a and 168b (FIG. 5) straddling the main rail 30 and interconnecting end walls 170a and 1701; extending under the main rail. Extensionsof the end walls of mounting frame 166 provide the brackets 27 for pivotally connecting the drafting head 26 to the main carriage 28.

Each main carriage frame sidewall is formed with an upstanding boss 174, each mounting a roller 176, as best seen in FIG. 6. These rollers roll on the top surface of the channel-shaped main rail 30 to support and guide the main carriage 28 for movement therealong. To further guide the main carriage during its transverse movement, frame sidewall -168b mounts a pair of rollers 178 which rideagainst'the outersurface of depending side portion 300 of main rail 30, as seen in FIGS. 5 and 6. Each main carriage frame end wall mounts a roller 180 which rides against the inner surface of main rail side portion 30a. In addition, eachv carriage frame sidewall mounts a roller 182 which rides against the bottomedge surface of depending main rail side portions 30a and 30b. v

It is thus seen that the various rollers of the main carriage 28 working against the surfaces of the main rail '30 serve to mount and precisely guide the main carriage during its transverse movement. Preferably, the various carriage rollers, including the upper and lower carriage rollers previously described, are mounted in eccentric bearings which are adjustable so as to precisely position the roller axes and thereby remove any play in the mountings of the various carriages to their respective rails. 7

As best seen in FIGS. 2A and 5, cross shafts 98 and 112 pass freely through clearance holes 190 in a'block 192 carried by each main carriage frame end wall 170a and 170b. Blocks 192 serve to mount separate bearings 194, with the cross shafts 98.and 112 passing freely therethrough. It is seen in FIG. 7 that these bearings are adapted to journal end caps 196 which engage and maintain the halves of a split sleeve 198 in circumferential relation to each cross shaft, extending coaxially therethrough. Split sleeves 198 are preferably formed of a phenolic bearing material and have their bores appropriately keyed to engage elongated splines formed in the cross shafts (FIG. 6).

It is thus seen that upon rotation of either cross shaft, driving rotation is imparted to its associate split sleeve 198 and yet the split sleeve is capable of-sliding longitudinally on its cross shaft. 1

Again as seen in FIGS. 5-7, split sleeve 198 about transverse cross shaft 98 mounts and rotates a helical ring gear 200. Similarly, split sleeve 198 about longitudinal cross shaft 112 mounts and rotates a second helical ring gear 202. Helical ring gear 200 is adapted for meshing engagement with a helical gear 204 carried by a shaft 206 joumalled at each end in main carriage frame sidewalls 168a and 168b. Inwardly of frame sidewall 168b, shaft 206 carries a pinion gear 208, which is adapted for meshing engagement with a gear 210 carried on a shaft 212 joumalled in frame sidewalls 168a and 168b. inwardly of frame sidewall member 168a, shaft 212 also mounts a pinion-gear 214 adapted for meshing engagement with an elongated circular pitch rack gear216 mounted by and coextensive with main rail depending side portion 30b, as best seen in FIGS. 2A and 6.

It is thus seen that rotation of the transverse cross shaft 98 is'coupled through gears 200, 204, 208, 210 and 214 to rackgear 216 to thereby produce transverse movement of the main carriage 28 on main rail 30.

Again referring to FIGS. 2A, 5 and 6, helical ring gear 202 mounted on and rotated by the split sleeve 198 about longitudinal 'cross shaft 112 is adapted for meshing engagement with a helical gear 220 carried on a shaft 222 joumalled in main carriage frame sidewalls 168a and 168b. Thus, rotation of the longitudinal cross shaft 112-is coupled to shaft 222 at a right angle thereto by the helical gears 202 and 220. It is important to note however that the gear trains between the cross shafts 98 and 112 and the main carriage 28 are bi-directional in nature, and thusrotation of shaft 206 in'the main carriageimparts rotation to the transverse cross shaft 98, while rotation of shaft 222 in themain carriage imparts rotation to longitudinal cross shaft'112.

It is seen in FIG. 5 that shaft 206 extends beyond the main carriage frame sidewall 168a and is fitted with a handwheel 230 facilitating manual rotation of shaft 206 which, in addition to rotating transverse cross shaft-98, rotates pinion gear 214 meshing with rack 216. As a result, transverse movement of the main carriage 28 on main rail 30 may be manually motivated by rotation of transverse handwheel 230. The other end of shaft 206 extends through and beyond main. carriage frame sidewall 168b and mounts a pair of graduated readout dials 232 and 234. Dial 232 is preferably graduated'in 0.010 inch increments around its periphery, while dial 234 is graduated in the scale to which the draftsman-is working. Thus, dial 234 is preferably readily removable, so that different dials graduated in various drawing scales may be substituted. A bracket 236 secured to carriage frame sidewall 1681; is formed having a laterally extending arm 236a which projects betweendials 232 and 234. A benchmark 238 inscribed on' bracket arm 236a facilitates reading of the scale graduations on dials 232 and 234.

Referring to FIG. 8, dial 232 is a cup shaped member carried on a hub 240 locked to shaft 206 by a set screw 241. The right end portion of hub 240 is threaded to receive a nut 242. A thrust washer 244 is introduced between nut 242 and the radial end wall of dial232 to press the dial end wall against the raised central body portion of hub 240. By virtue of this construction, dial 232 rotates with shaft 206 to provide a readout in inches of the distance of transverse movement of the main carriage 28, and yet may be readily angularly reoriented on shaft 206 without disturbing the shaft angular orientation. This arrangement is desirable so as to facilitate resetting dial 232 to align the zero of its scale with bench mark 238 and thereby simplify the reading of the scale pursuant to achieving a desired increment of transverse movement of drafting head 26 by rotation of transverse handwheel 230 or stepping motor 50. Thus, the draftsman need not scale off a desired increment of transverse movement but merely, in effect, dial in the desired increment by rotation of handwheel 230 while observing the scale on dial 232.

Dial 234 is, like dial 232, cup shaped and is removably mounted on a second cup-shaped member 246 carried by hub 240. The left end portion of hub 240 is threaded to receive a nut 242 which lightly frictionally clamps the end wall of mounting cup member 246 between another thrust washer 244 and the raised central body portion of hub 240. Thus, dial 234 is rotated by shaft 206 and may also be readily angularly re-oriented to zero the scale carried thereby with reference to bench mark 238 without altering the angularly orientation of shaft 206. As previously noted, the scale on dial 234 is preferably graduated in accordance with the scale size to which the draftsman is working. Consequently, dials 232'and 234 respectively provide a readout of the actual distance of transverse movement of the drafting head and the distance of transverse movement translated to the prevailing drawing scale. Alternatively, either or both dials 232 and 234 may be graduated in fractional inch increments.

Returning to FIG. 5, main carriage shaft 222 extends through and beyond frame side member 168b and mounts a pair of dials 250 and 252 in the identical manner as dials 232 and 234 are mounted on shaft 206. Dial 250 provides a readout of the actual distance of longitudinal movement of the main rail 30 and main carriage 28 motivated by a longitudinal handwheel 253 secured on the other end of shaft 222 or motor 50, while dial 252 is graduated to provide an instant conversion of the longitudinal movement of the drafting head to the prevailing drawing scale.

The operation of the automatic drafting machine, wherein longitudinal and transverse movements of the drafting head 26 are motivated by stepping motor 50 in accordance with numerical inputs imposed on a decade array of digital input switches 41 included in the numerical control input unit 40, will now be described in connection with FIG. 9. The input switches 41 may take various forms, including that of a keyboard. These digital inputs indicating the desired distances the drafting head 26 is to be moved in the longitudinal and transverse directions are supplied to a stepping motor control network 260 which operates to translate the digital inputs into appropriate numbers of pulses; each pulse being effective to step the stepping motor 50 through a discreet increment of output shaft rotation.

In typical numerical control stepping motor control networks there is provided for the convenience of the user switched external terminals to which connection may be made for external control components in order to facilitate synchronizing the operations of the external components to the operation of the motor control network 260. Thus, as shown in FIG. 9, external leads 262 are shown connected to a relay 264 whose contacts, indicated at 266, are connected in the energization circuit for a timing motor 268. In accordance with the operating convention adopted in the illustrated embodiment, relay 264 is energized to close its contacts 266 at all times except during an execution of an indexing function, during'which stepping pulses are supplied to stepping motor 50. Thus, during an indexing function, relay 264 is de-energized by the motor control network 260.-

In one type of motor control network supplied by the Superior Electric Company, relay 264 and its contacts 266 are supplied internally, and thus the energization circuit for the timing motor 268 is simply connected directly to the appropriate output terminals of the motor control network 260. I

Still referring to FIG. 9, the numerical control input unit 40 includes four directional control switches, indicated at UP, DN, RT and LT. Up switch UP is closed to initiate indexing movement of the drafting head upwardly along the transverse axis toward the top of the drafting board 20. Depression of down switch DN initiates indexing movement of the drafting head along the transverse axis toward the bottom of the drafting board. Similarly, switch RT initiates indexing movement of the drafting head along the longitudinal axis to the right over a distance represented by the digital input switches 41, while depression of switch LT initiates indexing movement along the longitudinal axis toward the left over the same distance. The four directional control switches are electrically connected in parallel with each other and in common across busses 270 and 272 through a normally closed cam actuated switch CS1. Each directional control switch controls the energization of a separate control relay lCR, 2CR, 3CR and 4CR. Each control relay has a first set of relay contacts lCR-l, ZCR-l, 3CR-l and 4CR-l, respectively, which close upon relay energization initiated by enclosure of its associated directional control switch to establish a holding circuit through a normally open cam actuated switch CS2 to bus 270. These holding circuits sustain energization of their associated control relays and thus sustain an indexing function despite momentary closure of the associated one of the directional control switches.

In practice, the various directional control switches preferably take the form of a four position switch, indicated at 274 in FIG. 2A. The actuating lever of this switch is pushed up to close the UP switch contacts and down to close the DN switch contacts. Movement to the left closes the LT switch contacts and to the right closes the RT switch contacts seen in FIG. 9. There is thus provided in a sense directional correlation between the manipulation of the four position directional control switch 274 at the numerical control input unit 40 and the desired direction of movement of drafting head 26.

. the drafting head 26.

Still referring to FIG. 9, a second set of relay contacts for each control relay, indicated at 1CR-2, 2CR-2, 3CR-2, 4CR-2, are mutually connected in parallel in the energization circuit for timing motor 268. These.

second sets of control relay contacts are normally open, but upon energization of any one of the various control relays, the associated one set closes to' complete the energization circuit for timing motor 268' which rotates a bank of five switch cams 280-284 jointly mounted on the timing motor output shaft, schematically indicated at 286. Switch cam 280 controls the actuation of cam switch CS1 which, as already noted, is connected in series with each of the directional control switches. Switch cam 281 controls the actuation of CS2 which, as already described, is connected in series with each of the control relays and their respective holding circuit contacts 1CR-l,2CR-l,3CR-l and 4CR-l.

The relative angular orientations of the switch cams 280-284 at the beginning of an indexing function are essentially as shown in FIG. 9. Cam switch CS1 is normally closed when its cam follower actuating arm rides in recess 280a of switch cam 280. Thus, prior to an indexing function, the various directional control switches are activated by the closed condition of cam switch CSLIUPOH closure of one of the directional control switches, the associated control relay is energized and closure of its second set of relay contacts completes the energization circuit for timing motor 268. At the conclusion of the initial of rotation of switch cam 281 the cam follower actuating arm for cam switch CS2 rides out of cam recess 281a, effecting closure of its contacts and completion of the holding circuitfor the energized control relay through its now closed first relay contact set. At the conclusion of of rotation of the switch cam bank, the cam follower arm of cam switch CS1 rides out of recess 280a, opening its contacts and disabling all ofthe directional control switches.

As yet, the motor control network 260 has not initiated an indexing function, and thus relay contacts 266 remain closed for continued energization of timing motor 268. Each control relay is provided with a third set of relay contacts, indicated at lCR-3, 2CR-3, 3CR 3 and 4CR-3, which are connected in series withthe two clutches 74 and-76 across the busses 270 an 272. Specifically, control relay contacts lCR-3 and 2CR-3 are connected in par'allelto control the energization of transverse clutch 74, while control relay contacts 3CR 3 and 4CR-3 are connected in parallel to control the energization of longitudinal clutch 76. Thus, upon closure of either of the directional control switches UP or DN, either control relay lCR or 2CR is energized, and its associated contacts lCR-3 or 2CR-3 immediately close to energize and thus engage clutch "I4 preparatory to transverse movement up or down of the drafting control relay contacts 1CR-4, 2CR-4, 3CR-4 and 4CR- 4. Specifically, control relay contacts lCR-4 and 2CR- 4 are connected in parallel to permit energization and thus disengagement of transverse brake 82 upon closure of cam switch CS3. Similarly, control relay contacts 3CR-4 and 4CR-4 are connected in parallel to permit energization and thus disengagement of longitudinal brake 88 upon closure of cam switch contacts CS3. After completion of approximately the initial 150 of rotation of switch cam 282, the cam follower actuating arm of cam switch CS3 falls into recess 2824, permitting energization and disengagement of the appropriate brake in accordance with which one of the various directional control switches has been closed. As yet, the motor control network 260 has not been signaled to execute an indexing function, thus relay contacts 266 remain closed for continued energization of timing motor 268.

Directional control inputs to the motor control network 260 are developed on input lead 290 under the control of a fifth set of relay contacts 2CR-5 and 4CR-5 included with control relays 2CR and 4CR, respectively. If either the down switch DN is closedto call for movement of the drafting head 26 downward in the transdirection or theleft switch LT is closed to call for longitudinal movement of the drafting head to the-left,-

' oneof control relay, contacts 2CR-5 and 4CR-5 closes head 26, as the case may be. By the same token, closure trol the-energization of the transverse and longitudinal brakesf82 and 84, respectively, through a fourth set of to connect the directional control input lead 290 for motor. control network 260 to ground. This is interpreted by the motor control network as a command to rotate the stepping motor in a first direction which, by virtue of the gear trains employed, produces either downward transverse movement or leftward longitudinal movement of the drafting head. On the other hand, if either the up switch UP or the right switch RT is closed, the directionalcontrol input lead 290 forthe motor control network 260 is left floating, and this is interpreted as a command to rotate the stepping motor in the opposite direction which, as is now apparent, produces either upward transverse movement or rightward longitudinal movement of the drafting head 26.

Reflecting brieflyon the operation of the control circuit of FIG. 9 considered thusfar, closure of one of the directional control switches initiates energization of its associated control relay, which, in turn, operates to complete an energization circuit for timingmotor 268 thereby initiating rotation of the switch cam bank. De-

pending upon which of the control relays is energized, the appropriate directional control .input signal is developed on input lead 290 to the motor control network 260. Carn switch CS2 closes to complete the holding circuit for'the energized control relay through one of its own relay contacts and then cam switch CS1 opens to deactivate the directional control switches. The energized control relay also selects the appropriate one of clutches 74and 76 for energization and engagement to couple the stepping motor output shaft to the appropriate gear train for either-longitudinal or transverse movement of the drafting head. Cam switch CS3 then closes under the control of switch cam 282 and the energized control relay determines which of brakes 82 and 88 is to be energized and thus released.

At this point, all of the appropriate conditions are met for initiating an indexingfunction. After approximately 160 of rotation of the switch cam bank, the cam follower switch actuating arm for cam switch CS4 rides into recess 283a in the periphery of switch cam 283. The contacts of cam switch CS4 are connected to an index command input lead 292 for the stepping motor control network 260. Upon closure of the normally open cam switch contact CS4, a ground signal is impressed on index command input lead 292, signaling the motor control network to initiate an indexing function. As the indexing function is initiated, relay 264 is de-energized, and its contacts 266 drop out to de-energize the timing motor 268. to

Upon completion of the indexing function, relay 264 is again energized, its contacts 266 close and timing motor 268 is re-energized. After approximately 220 of rotation of the switch cam bank, the cam follower switch actuating arm for cam switch CS3 rides out of recess 282a, and its contacts open to break the energization circuit to the brakes 82 and 88. thus, immediately before and after execution of an indexing function, the brake which was disengaged to permit the indexing function is engaged to prevent spurious movement of the drafting head. It is observed that while the drafting head is being moved in the longitudinal direction, for example, the transverse brake 82 is engaged to prevent inadvertent transverse movement of the drafting head while it is being indexed in the longitudinal direction, and vice versa. After approximately 350 of rotation of the switch cam bank, the cam follower arms for cam switches CS1 and CS2 ride into their associated switch cam recesses. Cam switch CS2 opens to break the energization circuit to the particular control relay which had been energized and incidentally the energization circuit for timing motor 268, while cam switch CS1 closes to again activate the directional control switches in preparation for the next indexing function.

in many cases it may be desirable to manually override the automatic operation of the drafting machine of the present invention and move the drafting head 26 manually, either by rotation of handwheels 230 and 253 or simply by grasping the drafting head 26 and directly positioning it. To this end, there is provided a transverse brake release switch TBR which shunts both the cam switch CS3 and the parallel control relay contacts 1CR-4 and 2CR-4 to permit direct energization and release of the transverse brake 82. Similarly, a longitudinal brake release switch LBR shunts the cam switch CS3 and control relay contacts 3CR-4 and 4CR- 4 to permit direct energization and release of the iongitudinal brake 88.

As an additional feature of the invention, a fifth switch cam 284 is included in the switch cam bank rotated by timing motor 268. This switch cam controls the actuation of a cam switch CS5 whose contacts are connected in series with a double index switch DI across the contacts of cam switch CS4. It will be recalled that closure of cam switch contacts CS4 generated the index command input signal on lead 292 to the stepping motor control network 260. As will be seen, if the double index switch DI is closed, it arms cam switch CS5 to generate a second index command input signal on lead 292 and the stepping motor 50 is indexed again by the amount set into the digital input switches 41. More specifically, it will be recalled that after rotation of switch cam 283 through approximately of rotation, cam switch CS4 closes to generate the index command input signal on lead 292. Energization to the timing motor 268 is broken by relay contacts 266 until this first indexing function is concluded. Relay 264 is then again energized, and the energization circuit to the timing motor 268 is re-established. With an additional 10 of rotation of switch cam 293, the cam follower actuating arm for cam switch CS4 rides out of recess 283a causing its contacts to open. After approximately 200 of rotation of the switch cam bank, the

cam follower actuating arm for cam switch CS5 rides into the recess 284a in switch cam 284 and its contacts close to connect the lead 292 through the closed double index switch D1 to ground. There is thus generated a second index command input signal to the stepping motor network 260 which responds by controlling the stepping motor 268 to execute a second indexing movement in the same direction and through the same distance as the first indexing movement initiated by closure of cam switch CR4.

It is thus seen that upon closure of the double index switch, the draftsman immediately doubles the-drawing scale he is working to. Similarly, he can maintain the double index switch DI closed and instantaneously reduce the drawing scale he is working to by one-half merely by opening the double index switch.

This feature is particularly advantageous in mechanical drafting of round parts with the double index switch DI closed. Then, when the draftsman has located the center line of the round part, he merely enters its diameter on the digital switches 41 and opens the double index switch DI. Upon closure of the appropriate directional control switch, the drafting head automatically moves a distance equal to the radius of the part. By the same token, if the draftsman locates the peripheral surface of the round part, he can initiate a single index function after entry of the diameter of the part to precisely locate the center line oraxis thereof.

It will be recalled from the foregoing description that the automatic numerical control drafting machine of FIG. 1 can be readily operated in a manual mode. This is achieved simply by closure of the brake release switches TBR and LBR shown schematically in FIG. 9 and located at the numerical control input unit 40. Specifically, if the draftsman wishes to manually index the drafting head in the transverse direction, he closes the switch TBR to release the transverse brake 82. The draftsman then simply dials in the distance he wishes to move the drafting head 26 in the transverse direction by rotation in the appropriate direction of handwheel 230 while obtaining a continuous readout of the transverse movement from dials 232 and 234. It will be noted from FIG. 9 that since none of the directional control switches have been depressed, the transverse clutch 74 is not engaged, and thus the transverse driving power introduced via handwheel 230 is not coupled to the stepping motor 50. Preferably while manually moving the drafting head in the transverse direction, the longitudinal brake release switch LBR is left open to maintain the longitudinal brake 88 engaged, thus preventing inadvertent movement of the drafting head in the longitudinal direction while it is being positioned in the transverse direction.

Similarly, if manually motivated longitudinal movement of the drafting head 26 is desired, the longitudinal brake release switch LBR is closed while leaving the transverse brake release switch TBR opened. This releasesthe longitudinal brake 88 while maintaining the transverse brake 82 engaged. The desired increment of longitudinal movement is then dialed in by rotation of the longitudinal handwheel 253 while observing the scales of either of dials 250 and 252 (FIG. Also as previously noted, one or both of the brake release switches TBR and LBR may be closed and the drafting head 26 positioned merely by manual pressure on the drafting head itself.

This suggests that many of the features of the drafting machine of the present invention may be achieved in a strictly mechanical version of the invention. Obviously,.a manually actuated embodiment would permit the elimination of stepping motor 50, clutches 74 and 76, brakes 82 and 88, stepping motor control network 260 and the numerical control input unit40. In addition, the longitudinal and transverse drive gear train between the stepping motor and the cross shafts 98 and 112 are unnecessary. Moreover, since the longitudinal and transverse drive inputs are introduced at the'main carriage 28, the transverse cross shaft '98 can also be eliminated. It will be appreciated that the elimination of all of these components will amount to a considerable cost savings to the purchaser.

The essential differences between the automatic numerical control drafting machine and the purely mechanical version are reflected in the sectional viewof FIG.- which-corresponds to. the sectional view of FIG. 5. Like parts are given corresponding reference numerals in FIG. 10. To translate the drafting head 26 in the longitudinal direction, longitudinal handwheel 253 is rotated and this rotational input is coupled through the helical gear 220 on the handwheel shaft 222 and the helical ring gear 202 fitted on split sleeve 198 to the longitudinal cross shaft 112, and thence through the gearing at'each end of the longitudinal cross shaft in the upper and lower carriages 32 and 38 to the rack gears 122 and 154 carried by top and bottom rails 34 and 36, which gearing is identical to that previously described in connection with the automatic numerical control drafting machine embodiment of the invention.

For transverse movement of the drafting head, rotation of handwheel 230 is coupled through gears 208, 210, shaft 212 and gear 214 to rack gear 216 carried by main 'rail 30..S ince transverse driving power .is not.

brought in externally of the main carriage 28, but originates either by rotation of handwheel 230 or through pressure exerted on the drafting head which is connected to the main carriage, transverse cross shaft 98 in unnecessary and thus is eliminated from FIG. 10.

Since the manual drafting machine embodiment of lever 304 is pivotally mounted on a pivot post 306 carried by frame sidewall 168b and is formed with a brake shoe tip 308 adapted for frictional engagement with the periphery of brake drum 300. Similarly, brake drum 302 is engaged by a brake shoe tip 308 carried by a brake operator lever 312 mounted on a second pivot post 306 carried by frame sidewall 1681:. As best seen in FIG. 10, the frame sidewall 168b is formed with a groove 316 vertically aligned with each pivot post 306.

A spring 318 is accommodated in each groove 316 and 1 urges a ball 320 secured to its upper end upwardly againstthe under surface of a lateral extension of each brake operator lever 304 and 312 overlying the upper edge of the main carriage frame sidewall 168b. The bottom edge of each of these lateral extensions engaged by the upwardly spring biasedballs 320 is V- shaped, as indicated at 322 in FIG. 11, to thus provide a toggling characteristic to the operation of the brake operator levers 304 and 312.

As best seen from FIG. 11, lever 304 has been pivoted in the counterclockwise direction to engage its brake shoe tip 308 against the periphery of brake drum 300. Ball 320 engages the right side of the V-shaped edge 322 to retain the lever 304 in its operative, brake engaging position. When lever 304 is pivoted inthe clockwise direction about pivot post 306, ball 320' depresses and rides over the apex of the V-shaped edge surface 322, whereupon it is effective to position the lever against a stop post 324 carried by the main carriage frame sidewall 168b. The brake operator lever 304 is thus retained in its inoperative, brake disengagthe present invention preferably does not include electrically'actuated braking, it is preferred to provide mechanically actuating braking to hold the drafting head in a desired position. Accordingly, as seen in FIG. 11, the transverse handwheel shaft 206 is adapted to mount abrake drum 300 adjacent the outer surfaceof I sidewall 168b 'of the main carriage mounting frame 166. Similarly, a brake drum 302 is mounted on the longitudinal handwheel shaft 222. A brake operator ing position.

I Still referring to FIG. 11, the longitudinal brake operator lever 312 is showntoggled to its inoperative position with its brake shoe tip 308 disengaged from the periphery of its brake drum 302 and its right side edge bearing against a second stop post 324. It is thus seen that the brake operator levers.304 and 312 are readily toggled by simple finger pressure to selectively brake and release the main carriage 28 for longitudinal and/or transverse movement.

It has been found that due to the freely movable character of the mounting of the main carriage on the main rail,, as well as the main rail carriages on the top and bottom rail, it is desirable to provide a system for counterbalancing the weight of the main carriage 28 and drafting head 26 when the drafting table 20 is tilted, such as illustrated in FIG. 1. Otherwise, when the transverse electrical-brake 82 in the automated embodiment or the transverse mechanical brake, consisting of brake drum 300 and brake operator lever 304, in the manual embodiment is released to permit transverse positioning of the drafting head, the main carriage will move toward bottom rail 36 under gravity unless restrained by the draftsman. To overcome this problem there is provided, as seen in FIG. 12, a counterweight 330 which is effectively coupled to the main carriage 28 by a cable 332. The counterweight 330 mounts a roller 334 which rides on a side rail 335 exto the main rail and the top and bottom rails guarantees line parallelism over the entire drafting surface, even to the point of withstanding inadvertent pressures exerted by the draftsman. The braking feature prevents inadvertent movement of the drafting head.

It is contemplated that the principles of the present invention may be adapted to a point coordinate locator with a cross-hair viewer substituted for the drafting head. From a zero coordinate position, the viewer is moved to align its cross-hair with the point whose coordinates are to be determined. The extent of movement in the transverse (Y) and longitudinal (X) directions to the point may be read from the readout dials or from a suitable distance readout device geared to the viewer in the manner that the stepping motor 50 is geared to the drafting head in the disclosed automatic drafting machine embodiment.

It will thus be seen that the objects set froth above,

tion or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A drafting machine comprising, in combination:

A. a carriage having means for attaching it to a drafting head;

B. an elongated main rail mounting the carriage for linear movement in either direction parallel to a first orthogonal axis over a drafting surface, said main rail having a first rack gear carried by and substantially coextensive with the rail;

C. a pair of guide rails respectively supporting said main rail at its opposite extremities for lateral movement in either direction parallel to a second orthogonal axis perpendicular to the first, at least one of said guide rails having a second rack gear substantially coextensive with that guide rail;

D. a first drive train for effecting movement of said carriage along said first axis, said first drive train comprising a first pinion gear secured to said carriage and engaging said first rack gear;

E. a second drive train for effecting concurrent movement of the extremities of said main rail along said guide rails and comprising a second pinion gear secured to said main rail and engaging said second rack gear;

F. a single motive means for driving both the first and second drive trains; and

G. coupling means operable selectively to drive 6 either said first or said second drive train from said motive means, said coupling means comprising 1. a first clutch energizable to couple the driving output of said motive means to said first pinion gear, and

2. a second clutch energizable to couple the driving output of said motive means-to said second pinion gear alternatively to but not concurrently with its coupling to the first pinion gear.

2. The drafting machine defined in claim 1, which further comprises:

A. a first handwheel supported by said carriage and drivingly coupled to said first pinion, said first handwheel being operable, when said first clutch is deenergized, to move said carriage in a direction parallel to said first axis, and a second handwheel supported by said carriage and drivingly coupled to said second pinion by way of an elongated shaft aligned with said main rail and fixedly supported thereon, said second handwheel being operable, when said second clutch is deenergized, to move said main rail laterally in a direction parallel to said second axis.

3. A drafting machine comprising, in combination: A. a carriage having means for attaching it to a drafting head capable of being moved by the carriage; B. an elongated structure mounting said carriage for linear movement thereon in either direction paral lel to a first orthogonal axis over a drafting surface;

C. means supporting said elongated structure at its opposite ends for linear movement on said supporting means in either direction parallel to a second orthogonal axis perpendicular to the first;

D. a first drive train for effecting movement of said carriage along said first axis and a second drive train for effecting movement of said elongated structure along said second axis, whereby to position a drafting head attached to the carriage at any desired point over the drafting surface;

E. a single motive means for driving both the first and second drive trains, and I F. coupling means operable selectively to connect said motive means to drive either said first or said second drive train, said coupling means comprisl a first clutch energizable to couple the driving output of said motive means to said first drive train, and

2. a second clutch energizable to couple the driving output of said motive means to said second drive train alternatively to but not concurrently with its coupling to the first drive train means.

4. A drafting machine according to claim 3 in which said motive means is a stepping motor and in which there is provided A. a numerical input unit for expressing alternatively the distance said carriage is to move in either direction on said elongated structure or the distance said elongated structure is to move on said supporting means in either direction along said second axis; and

B. a motor control network for translating the distance expressed at said numerical input unit into corresponding numbers of energizing pulses for application to said stepping motor to index said stepping motor accordingly.

5. The drafting machine defined in claim 4, which further'includes:

carriage 32. This spool serves as a take-up and play-out 4, cable 332 extends downwardly and around a vertically oriented pulley 338 mounted at the lower end of I secondary mounting plate 94. From pulley 338, the

cable 332 extends horizontally and around a horizontally oriented pulley 340 mounted at the lower end of mounting plate 60. Then as seen in FIG. 4, the cable runs to the left along top rail 34 and around a pulley 342 journalled on a shaft 344 mounted at its ends in the upper and lower lateral extensions of top rail 34 (also seen in FIG. 12). From pulley 342,,the cable 332 extends around a pulley 346 mounted by the counterweight 330 and back around a second pulley 348 journalled on pulley shaft 344. Then, as seen in FIG. 4, the cable extends along the entire length of top rail 34 and around apulley 350 mounted at the other end thereof,

returning to the upper main rail carriage 32 where its end is secured to mounting plate 60, as indicated at 352.

From the foregoing description it is seen that when main carriage 28 moves transversely downward on main rail 30, spool 336 is rotated by transverse cross shaft 98 in'a direction to take up the cable 332, and the counterweight 330 moves upwardly on side rail 335 toward top rail 34. Conversely, when-the main carriage moves transversely upward, spool 336 is rotated by transverse cross shaft 98 to play out the cable and the counterweight 330 moves downwardly on side rail 335 toward bottom rail 36. Thus the weight of the main carriage and drafting head acting in the transverse .direction is effectively counterbalanced by counterweight 330, and the transverse position of the drafting head is maintained when the transverse brake is removed.

On the other hand, when the main rail moves longitudinally, it is seen that each end of cable 332'is fixed to the upper main rail carriage 32, and thus the cable is effectively played out from the side of the upper carriage in the direction of its movement and simultaneously taken up-at the opposite side of the upper main rail carriage. Thus,- during longitudinal movement of mainrail 30 the counterweight 330 does not move on side rail 335 and offersno counterforce to longitudinal positioning of the drafting head 26.

It will be observed that by virtue of mounting the counterweight:330 on side rail 335, its counterbalancing effect to the forces of gravity on the main carriage and drafting head is automatically adjusted 'in accordance with the degree of tilt of drafting board 20. Specifically, if the drafting board is perfectly horizontal, there is no force. of gravity due. to the weight of main carriage 28 and drafting head 26 aligned with main rail 30, and thus there is nonecessity for counterbalancingPreferably, as seen in FIG. 12, side rail 335 is provided with a slight inclination by virtue of its mounting between the top and bottom rails such that counterweight 330 does exert a slight counterbalancing force in theabsence of drafting board tilt-to somewhat compensate for the slight frictional losses in the transverse drive train and the slight drag of the drafting head 26 on the draftingsurface 24. When the drafting board is tilted,- the side rail 335 is inclined a corresponding amount to automatically increase the counterbalancing effect of counterweight 330 to the increased gravity force component acting on-the main carriage and drafting head which is aligned with main rail 30 in the transverse downward direction. The weight of the drafting head and main carriage can thus be substantially perfectly counterbalanced such that when the transverse brake 82 is released, the main carriage and drafting head do not move transversely downward under the influence of gravity.

In the manual embodiment of the invention, as best seen in FIG. 10, there is no transversecross shaft and thus a different technique for coupling the counterweight 330 to the main carriage 28 must be employed. Specifically, the cable, indicated at 360, is in the form. of a continuous loop, which is wrapped arounda pulley 362 mounted by the main carriage 28. Both reaches of cable 360 from pulley 362 extend toward the upper main rail carriage 32 and around a pair of upper and lowervertically aligned pulleys 364 and 366 carried by the secondary mounting plate 94. The lowerpulley of From this pulley the cable extends around pulley 346' carried by counterweight 330 and back around a second pulley corresponding to pulley 348 in FIG. 12, and then along the length of top rail 34-toa pulley at the other end corresponding to pulley 350 in FIG. 4. From pulley 350, the cable returns to pulley 370 in FIG. 10, completingits loop path. l

' The counterweight system for the manual drafting machine operates in the same manner as the counterweight system already described for the automatic drafting machine. Specifically, when the main rail 30 moves longitudinally, the position of counterweight 330 on siderail 335 is unchanged. On the other hand, when the main carriage 28 moves transversely of the drafting surface 24 on main rail 30, the length of the cable loop between the main carriage and the main rail upper carriage 32 either increases, drawing the counterweight 330 toward top rail 34, or decreases, allowing the counterweight to move toward bottom rail 36 on side rail 335.

From the foregoing description, it is seen that there is provided a drafting machine which, in eitherits 'rnanual or automatic numerical controlled embodiments, enables a draftsman to produce technical drawings more accurately and in less time than has been possible with currently available drafting machines. The draftsman need not point off dimensions using a separate scale, but instead merely enters the dimensions vvia digital switches 41 or dials in the desired dimensions using handwheels 230-and 253 and their associated readout dials to accurately prepare a drawing. Thus accuracy is not dependent on eyesight, steadiness of hand, and the ability to read fine scales. With appropriate setup, drawing scale enlargements or reductions can be obtained automatically with the draftsman having to resort to conversion tables and scales or to mathematical calculations. Thus errors are avoided and much of the tedium, as well as instrument manipulation and positioning, is avoided,

In the manual embodiment, the drafting head can be readily positioned to within 0.005 inch of the true posi- A. a control circuit including directional control switch means for selecting one of said first and second clutches for engagement, deriving a directional control input signal to said control network to indicate the appropriate rotational direction for said stepping motor output shaft, and initiating the application of an index command signal to said motor control network to execute an indexing function along one of said axes.

6. The drafting machine defined in claim 5, wherein' said control circuit further includes:

1. timing sequence control means actuated by said directional control switch means to delay the application of said index command signal to said control network until after said selected one clutch has been engaged and said motor control network has received said directional control input signal.

7. The drafting machine defined in claim 6, wherein said first drive input means includes a first brake and said second drive input means includes a second brake, and

1. said directional control switch means selects one of said brakes for disengagement, and

2. said timing sequence control means delays the release of said one brake until immediately prior to the application of said index command signal.

8. The drafting machine defined in claim 7, wherein said timing sequence control means further operates to re-engage said one brake upon conclusion of an indexing function and then to disengage said one clutch in preparation for the initiation of the next indexing function.

9. The drafting machine defined in claim 8, wherein said control circuit further includes a double index switch operating in conjunction with said timing sequence control means, immediately upon the conclusion of a first indexing function, to apply a second index command signal to said control network and thereby produce a second indexing function moving said drafting head in the same direction and over the same distance as was achieved during said first indexing function.

10. The drafting machine defined in claim 7, wherein said control circuit further includes a brake release switch for each said first and second brakes, thereby permitting individual and selective releases of said brakes independently of said directional control switch means and said timing sequence control means.

11. The drafting machine defined in claim 4, wherein each of said drive trains further includes at least one interchangeable gear set for establishing a predetermined relationship between the distance expressed by said numerical input unit and the lengths of movements of said drafting head parallel to said axes, whereby to automatically convert to a predetermined drawing scale.

12. A drafting machine comprising, in combination:

A. a main carriage having means for attaching it to a drafting head capable of being moved by the carriage;

B. an elongated main rail mounting said carriage for linear movement thereon in either direction parallel to a first orthogonal axis over a drafting surface;

' C. a pair of spaced parallel side rails for said machine arranged perpendicular to the main rail at its opposite extremities; D. secondary carriage means positioned at each end of the main rail and mounting the main rail on the side rails for lateral movement in eitherdirection parallel to a second orthogonal axis which is perpendicular to the first;

E. a single electric motor having an output shaft for providing motion-producing power to said main carriage and to said main rail;

F. first input drive train means for producing movement of said main carriage along said first axis and comprising 1 a first elongated rack gear carried by, and substantially coextensive with, said main rail,

2 a first pinion gear rotatably secured to said carriage and adapted for meshing engagement with said first rack gear, and

3 a first shaft rotatably supported on said main rail and extending from end to end of that rail,

4 a first clutch selectively coupling the output shaft of said motor to said first shaft, and

5 a first drive coupling slidably mounted with respect to said first shaft for coupling the rotation of said first shaft to said first pinion gear as said carriage moves along said main rail; and

G. second input drive train means for producing lateral movement of said main rail along said second axis and comprising i. a second rack gear mounted by, and substantially coextensive with one of said side rails,

a second pinion gear rotatably secured to one of said secondary carriage means and adapted for meshing engagement with said second rack gear,

3. a second shaft rotatably supported on said main rail and extending lengthwise of that rail, said second shaft being drivingly coupled 'to said second pinion, and

a second clutch for selectively coupling said motor output shaft to said second shaft. 

1. a second rack gear mounted by, and substantially coextensive with one of said side rails,
 1. said directional control switch means selects one of said brakes for disengagement, and
 1. timing sequence control means actuated by said directional control switch means to delay the application of said index command signal to said control network until after said selected one clutch has been engaged and said motor control network has received said directional control input signal.
 1. a first clutch energizable to couple the driving output of said motive means to said first pinion gear, and
 1. A drafting machine comprising, in combination: A. a carriage having means for attaching it to a drafting head; B. an elongated main rail mounting the carriage for linear movement in either direction parallel to a first orthogonal axis over a drafting surface, said main rail having a first rack gear carried by and substantially coextensive with the rail; C. a pair of guide rails respectively supporting said main rail at its opposite extremities for lateral movement in either direction parallel to a second orthogonal axis perpendicular to the first, at least one of said guide rails having a second rack gear substantially coextensive with that guide rail; D. a first drive train for effecting movement of said carriage along said first axis, said first drive train comprising a first pinion gear secured to said carriage and engaging said first rack gear; E. a second drive train for effecting concurrent movement of the extremities of said main rail along said guide rails and comprising a second pinion gear secured to said main rail and engaging said second rack gear; F. a single motive means for driving both the first and second drive trains; and G. coupling means operable selectively to drive either said first or said second drive train from said motive means, said coupling means comprising
 1. A drafting machine comprising, in combination: A. a carriage having means for attaching it to a drafting head; B. an elongated main rail mounting the carriage for linear movement in either direction parallel to a first orthogonal axis over a drafting surface, said main rail having a first rack gear carried by and substantially coextensive with the rail; C. a pair of guide rails respectively supporting said main rail at its opposite extremities for lateral movement in either direction parallel to a second orthogonal axis perpendicular to the first, at least one of said guide rails having a second rack gear substantially coextensive with that guide rail; D. a first drive train for effecting movement of said carriage along said first axis, said first drive train comprising a first pinion gear secured to said carriage and engaging said first rack gear; E. a second drive train for effecting concurrent movement of the extremities of said main rail along said guide rails and comprising a second pinion gear secured to said main rail and engaging said second rack gear; F. a single motive means for driving both the first and second drive trains; and G. coupling means operable selectively to drive either said first or said second drive train from said motive means, said coupling means comprising
 1. a first clutch energizable to couple the driving output of said motive means to said first pinion gear, and
 2. a second clutch energizable to couple the driving output of said motive means to said second pinion gear alternatively to but not concurrently with its coupling to the first pinion gear.
 2. The drafting machine defined in claim 1, which further comprises: A. a first handwheel supported by said carriage and drivingly coupled to said first pinion, said first handwheel being operable, when said first clutch is deenergized, to move said carriage in a direction parallel to said first axis, and a second handwheel supported by said carriage and drivingly coupled to said second pinion by way of an elongated shaft aligned with said main rail and fixedly supported thereon, said second handwheel being operable, when said second clutch is deenergized, to move said main rail laterally in a direction parallel to said second axis.
 2. a second clutch energizable to couple the driving output of said motive means to said second pinion gear alternatively to but not concurrently with its coupling to the first pinion gear.
 2. a second clutch energizable to couple the driving output of said motive means to said second drive train alternatively to but not concurrently with its coupling to the first drive train means.
 2. a second pinion gear rotatably secured to one of said secondary carriage means and adapted for meshing engagement with said second rack gear,
 2. said timing sequence control means delays the release of said one brake until immediately prior to the application of said index command signal.
 3. a second shaft rotatably supported on said main rail and extending lengthwise of that rail, said second shaft being drivingly coupled to said second pinion, and 4 a second clutch for selectively coupling said motor output shaft to said second shaft.
 3. A drafting machine comprising, in combination: A. a carriage having means for attaching it to a drafting head capable of being moved by the carriage; B. an elongated structure mounting said carriage for linear movement thereon in either direction parallel to a first orthogonal axis over a drafting surface; C. means supporting said elongated structure at its opposite ends for linear movement on said supporting means in either direction parallel to a second orthogonal axis perpendicular to the first; D. a first drive train for effecting movement of said carriage along said first axis and a second drive train for effecting movement of said elongated structure along said second axis, whereby to position a drafting head attached to the carriage at any desired point over the drafting surface; E. a single motive means for driving both the first and second drive trains, and F. coupling means operable selectively to connect said motive means to drive either said first or said second drive train, said coupling means comprising 1 a first clutch energizable to couple the driving output of said motive means to said first drive train, and
 4. A drafting machine according to claim 3 in which said motive means is a stepping motor and in which there is provided A. a numerical input unit for expressing alternatively the distance said carriage is to move in either direction on said elongated structure or the distance said elongated structure is to move on said supporting means in either direction along said second axis; and B. a motor control network for translating the distance expressed at said numerical input unit into corresponding numbers of energizing pulses for application to said stepping motor to index said stepping motor accordingly.
 5. The drafting machine defined in claim 4, which further includes: A. a control circuit including directional control switch means for selecting one of said first and second clutches for engagement, deriving a directional control input signal to said control network to indicate the appropriate rotational direction for said stepping motor output shaft, and initiating the application of an index command signal to said motor control network to execute an indexing function along one of said axes.
 6. The drafting machine defined in claim 5, wherein said control circuit further includes:
 7. The drafting machine defined in claim 6, wherein said first drive input means includes a first brake and said second drive input means includes a second brake, and
 8. The drafting machine defined in claim 7, wherein said timing sequence control means further operates to re-engage said one brake upon conclusion of an indexing function and then to disengage said one clutch in preparation for the initiation of the next indexing function.
 9. The drafting machine defined in claim 8, wherein said control circuit further includes a double index switch operating in conjunction with said timing sequence control means, immediately upon the conclusion of a first indexing function, to apply a second index command signal to said control network and thereby produce a second indexing function moving said drafting head in the same direction and over the same distance as was achieved during said first indexing function.
 10. The drafting machine defined in claim 7, wherein said control circuit further includes a brake release switch for each said first and second brakes, thereby permitting individual and selective releases of said brakes independently of said directional control switch means and said timing sequence control means.
 11. The drafting machine defined in claim 4, wherein each of said drive trains further includes at least one interchangeable gear set for establishing a predetermined relationship between the distance expressed by said numerical input unit and the lengths of movements of said drafting head parallel to said axes, whereby to automatically convert to a predetermined drawing scale. 